2 Mirror Image ?'s

Why can concave mirrors produce a real or virtual image, but convex mirrors can produce only one virtual image??

As well, when an object is moved along the principal axis towards the vertex of a concave mirror, the image changes. Where exaclty does this change occur and why? I know it has something to do with the paths of light rays and I think that it has something to do with how they are reflected, but if someone could clarify this for me it would be greatly appreciated!

Why can concave mirrors produce a real or virtual image, but convex mirrors can produce only one virtual image??

Is this because that in convex mirrors parallel light rays come togeather crpssing at a dingle focal point whereas concave mirrors cause parallel light rays to spread appart so that they appear to emmerge from the virtual focal point?